The busy signal has become less common in the past decade due to the prevalence of call waiting and voice mail.

Reasons for a busy signal

An otherwise unspecified busy signal indicates that the called number is occupied:

The called number is talking with another caller on the phone

The number is calling out,

Someone else has called the number or is calling the number at the same time,

The other line was left off-hook,

It is otherwise unavailable

The standard busy signal sometimes occurs (sometimes with an intercept message played over the busy) at the end of a call to indicate the other party has hung up, but mostly the Off-hook tone is used.

Reorder tone

A reorder tone, sometimes called a fast busy signal, indicates that no transmission path to the called number is available. This is usually because the Inter-LATA trunk is busy at the time of the call. Usually, this clears in a few seconds, if one redials.

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